ORGANIC I (Major's) LABORATORY
KELLY
SIMPLE AND FRACTIONAL DISTILLATION
I. PURPOSE:
To learn how to distill a miscible liquid mixture smoothly
and efficiently and to understand the limits of separation by
distillation.
II. ACTIVITIES:
Read : Landgrebe pp 142-157
We will work in pairs for this experiment. You may select your own
partner. Each pair will perform each of the following types of
distillation: (a) Simple distillation, (b) Fractional distillation - open column,
(c) Fractional distillation - ceramic saddles. This experiment will take two
lab periods to complete. You should complete one distillation the first
period and two the second period.
It will be necessary to regulate the boiling rate and read the
temperature and measure the volume distilled. Record, for your initial
temperature, the temperature after the first five drops distill and after
each two mL of distillate is collected. Record the data on the attached data
sheet.
As soon as the distillation is complete, transfer your data to the table
on the blackboard at the front of the lab. Before you leave the lab, be sure
to record ALL the data from the other distillation experiments. You will
need to average all the data for each type of distillation.
During the second lab period, we will learn about the graphical
presentation of data and plotting your data using the Macintosh computer.
You will plot, on one graph, the average boiling temperature (y axis) vs the
milliliters distilled (x axis) for each type of distillation. Use a different
color or type of line to differentiate between the plots. All axes and curves
must be clearly labeled.
IV. APPARATUS:
Simple distillation: The set-up is shown on page 65 except that the
water cooled condenser will be allowed to drip directly into a graduate
cylinder.
DISTILLATION
page 2
Note position of
thermometer bulb
Rubber bands
Note
Liquid
level
Boiling
chip
(a) Choose the distilling flask so that it is initially 30 to 60%
full. We will distill 40 ml of a 50:50 mixture of cyclohexane and
toluene (20 mL of cyclohexane and 20 mL of toluene) so use your
100 ml flask.
(b) Do not lubricate the joints. Ground glass joints should be
lubricated only for reduced pressure distillation. At atmospheric
pressure solvent enters the joints and dissolves out the lubricant
leaving a solid residue which may freeze the joints.
(c) It is customary to distill from left to right.
(d) Support the thermowell heater on a ring clamp leaving enough
space under the ring to allow lowering of the heater. Use 2
condenser clamps, one to support the distillation flask at it neck
and one on the water cooled condenser. Collect the product in a 10
mL graduated cylinder attached with a condenser clamp on a
second ring stand. Adjust the height of the graduated cylinder so
that it is just under the condenser outlet.
(e) Place a Boileaser chip in the flask to prevent bumping.
(f) Note the thermometer position in the figure on page 65. The top of
the thermometer bulb should be slightly below the bottom of the
side arm of the distilling head to accurately measure the
distillation temperature.
(g) Cooling water should enter at the bottom inlet of the horizontal
condenser and exit at the top inlet.
DISTILLATION
page 3
Fractional distillation:
(a) Use the wide-bore column as the vertical column ( in the fractional
distillation). Use the narrow-bore column for the horizontal
condenser (all distillations).
(b) The vertical column of the fractional distillation set-ups should be
packed loosely with glass wool or ceramic saddles and wrapped
with aluminum foil. If the column is packed too tightly, it will
flood (fill up with liquid) during the distillation and you will not
separate the liquids. The vertical column must NOT be water
cooled. it is appropriately call an air cooled fractionation column.
Columns specifically made for this purpose are shown on page 73.
(c) Get your lab instructor to approve your set-up before you begin
your distillation.
DISTILLATION
page 4
SAFETY PRECAUTIONS:
When your are ready to start the distillation, check the following items.
Then ask your lab instructor or assistant to approve your set-up. Failure
to do so could result in an accident.
1.
2.
3.
4.
5.
6.
7.
8.
V.
A boileaser should be in the distillation pot.
All joints should fit together without being under tension.
The distillation flask should be not more than 3/4 full.
No tight plugs of glass wool should occur in the fractionation
column.
The top of the thermometer bulb should not touch the glassware
and should be even with the bottom of the distillation head side
arm. The thermometer should fit tightly in the rubber holder.
The collecting vessel (10 ml grad. cylinder) should be close to the
exit from the condensing column.
Make sure that the vapor from the distillation flask can escape to
the atmosphere at the end of the apparatus (No closed System).
The heating mantle must be able to be lowered quickly to remove
the heat source without disturbing the integrity of the distillation
apparatus. If, at any time during your distillation, you have
doubts about the safety of your operation you should remove the
heat source. Not much can happen without it.
PROCEDURE
1. When you are ready to distill, turn the thermowell control to near
the highest setting. Reduce the power when the liquid begins to
boil so that it distills at a rate of approximately 1 drop per second.
It will be necessary to increase the power slightly during the
distillation as the lower boiling component is removed and the
distillation temperature increases.
2. Record the temperature when the first 5 drops of liquid fall from
the condenser into the graduated cylinder. Continue to record the
temperature after each successive 2 ml of distillate is collected.
Check often to see that the column does not flood. If it starts to fill
with liquid, reduce the heating rate.
3. Collect the following 3 fractions during the distillation in
labeled, stoppered glass vials provided by the assistant.
Save all three fractions for analysis in the next
experiment. Be sure they are securely stoppered or they
will evaporate during the week.
DISTILLATION
page 5
Fraction 1 - First 2 ml of distillate
Fraction 2 - Next 10 ml of distillate
Fraction 3 - Residue in the pot
Never distill to dryness. Leave about 1 ml of residue. Failure to do
so could result in an explosion or a cracked distillation flask.
4. Discard any distillate which is not to be save in the waste
bottle provided for this purpose. Never pour organic
liquids which are flammable and immiscible with water
down the drain.
III. LAB REPORT:
** Even though you worked in pairs, the lab report should
be an individual effort.
**
1. Title Page (your name and title of experiment)
2. Experimental Description. Explain the experimental procedure(s) in
your own words. Do Not just parrot the lab handout. Indicate
your partner on this page
3. Observations. Record any changes or problems which occur during
the distillation.
.4. Attach the data sheet to your report. Report your individual data
as well as the full class data
5. Attach your graphs of boiling point versus volume of distillate for
all four types of distillation.
6. Attach your answers to the questions
at the end of this
handout.
VI. QUESTIONS:
1
Arrange the fractionation types in their order of increasing
efficiency. Using your plot, state specifically how the plot leads
you to the above conclusion. This should require about a half a
page of discussion.
2. Indicate which types of distillation technique you performed.
What is the boiling point of pure cyclohexane and pure toluene?
Look them up in the "Handbook of Chemistry and Physics". At
what temperature did your distillation begin? Considering this, is
it likely that your initial distillate contained only cyclohexane?
Explain. What was the temperature at which you stopped our
distillations? Considering this temperature, is it likely that this
fraction contains only toluene? Explain.
DISTILLATION
page 6
3. The fractionation column makes possible a more complete
separation of these liquids than could be obtained in a simple
distillation. Describe what happens to the distillate on its way up
the fractionation column that improves the separation.
4. Refer to the boiling point diagram for butanol/acetone shown
below. Compound A = acetone; B=butanol
a. At what temperature would a solution containing 0.5 mole
fraction butanol and 0.5 mole fraction acetone begin to boil?
How does this temperature compare with the boiling points of
the pure compounds?
b. What would be the composition of the first droplet of vapor
which recondenses? How does this compare to the
composition of the liquid being distilled (0.5 mole fraction in
each component)? At what temperature will the droplet boil?
Will the vapor around the droplet be hot enough to cause the
droplet to boil?.
c.
How many times would you need to condense and reevaporate the first vapor to obtain pure acetone?
DISTILLATION
page 7
RECORD OF DISTILLATION
TEMPERATURES
mL
0.1
1
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
SIMPLE
OPEN COLUMN
avg
avg
SADDLES
avg
avg
0.
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48